EP0658984A2 - Codage perceptuel de signaux audio avec allocation des bits non-utilisés à un canal de données - Google Patents

Codage perceptuel de signaux audio avec allocation des bits non-utilisés à un canal de données Download PDF

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Publication number
EP0658984A2
EP0658984A2 EP94308909A EP94308909A EP0658984A2 EP 0658984 A2 EP0658984 A2 EP 0658984A2 EP 94308909 A EP94308909 A EP 94308909A EP 94308909 A EP94308909 A EP 94308909A EP 0658984 A2 EP0658984 A2 EP 0658984A2
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European Patent Office
Prior art keywords
signal
block
bits
audio
encoded
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EP94308909A
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German (de)
English (en)
Inventor
Sean Matthew Dorward
Jayant Nuggehally Sampath
James David Johnston
Schuyler Reynier Quackenbush
Kenneth Lane Thompson
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AT&T Corp
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AT&T Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0041—Arrangements at the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/66—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for reducing bandwidth of signals; for improving efficiency of transmission
    • H04B1/665—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for reducing bandwidth of signals; for improving efficiency of transmission using psychoacoustic properties of the ear, e.g. masking effect

Definitions

  • the present invention relates to the efficient utilization of allocated bandwidth of a transmission medium by a signal representing, for example, a digital audio signal.
  • PAC perceptual audio coding
  • a constant time portion of the audio signal with a lesser amount of perceptually relevant information requires fewer bits for a PAC system to encode than another constant time portion of the same audio signal with a larger amount of perceptually relevant information.
  • the first signal is comprised of a plurality of blocks, each representing a constant time portion of the first signal.
  • the plurality of blocks is denoted with the subscript "i.”
  • Each block is assigned a predetermined number N i , wherein N i is a maximum number of bits allowed to encode the i th block.
  • N i is a maximum number of bits allowed to encode the i th block.
  • the number of bits actually used to encode the i th block namely NU i
  • NA i represents the number of bits that are filled or inserted into the i th block in order to fully utilize the bandwidth allocated to the i th block.
  • NA i represents the difference between N i and NU i .
  • a second signal, "junk” data, or a combination of the two may be appropriately combined with the first signal to fill in areas in a digital output signal.
  • the digital output signal is comprised of a plurality of filled in blocks, each of which may be called a "superblock.” In other words, for each block, a superblock is formed. This results in a plurality of superblocks. If NA i is zero, the i th superblock and the i th block are identical. However, if NA i is not zero, NA i bits representative of the second signal, "junk" data, or a combination of the two are used, in conjunction with the NU i bits of the i th block, to form the i th superblock. Thus, the i th superblock always comprises N i bits.
  • the NA i bits typically, but not always, represent asynchronous information. To the extent that bits representing the second signal (as opposed to junk data) are available, they will be used to fill in the needed NA i bits in the i th superblock. However, the system will fill in, with junk data, the portion of the NA i bits that are not used by bits representing the second signal. Thus, for a given superblock having a non-zero value for NA i , the bits representing the second signal may vary from zero to NA i .
  • the invention allows for more efficient use of the allocated output rate of each superblock.
  • a system in which the invention may be implemented uses a transport layer assembler in the transmitter and a transport layer disassembler in the receiver that provide the plurality of superblocks with a certain amount of robustness to channel errors.
  • a system in which the invention may be implemented uses additional error protection schemes that make the plurality of superblocks more robust to channel errors.
  • a DAB system comprises a transmitter 10 and a receiver 20. Signals communicated from the transmitter 10 to the receiver 20 are transmitted in the terrestrial FM radio band (88-108 MHz).
  • the transmitter 10 comprises an audio interface 100, a perceptual audio encoder ("PAC") 250, a transport layer assembler 700, an error protection coder 800, an interleaver 900, a multiplexer 1000, a four-phase modulator 1100, a pulse shaper 1300, and an RF transmitter 1400.
  • PAC perceptual audio encoder
  • the receiver 20 comprises an RF receiver 1500, an equalizer 1600, a demodulator 1700, a second demultiplexer 1800, a deinterleaver 1900, an error protection decoder 2000, a transport layer disassembler 2200, a PAC decoder with error concealment 2400, and an audio interface 2900.
  • a stereo analog audio signal is applied to the audio interface 100.
  • Each audio channel of the stereo signal comprises a 0-20 kHz audio signal.
  • a clock signal is also input.
  • the interface converts each channel's audio signal to a digital signal by conventional analog-to-digital conversion techniques. In performing the conversion, the analog signals are sampled. Audio interface 100 produces digital stereo output signals conditioned for use by the PAC coder 250 and eventual use by the transport layer assembler 700.
  • the PAC coder codes the digital stereo output signals in a perceptual manner to generate a first signal 701.
  • the transport layer assembler 700 receives the first signal 701, e.g., a digital audio signal, from the audio interface 100 and a second signal 204, e.g., a auxiliary data signal from an asynchronous data signal source and generates the digital output signal at a time invariant allocated output rate. Illustratively, this rate is 160 kilobits/second (kbps).
  • This digital output signal comprises compressed audio information and auxiliary data.
  • the transport layer assembler 700 also serves to add ancillary data at a rate of, e.g., 10 kbps, to the 160 kbps time invariant allocated output rate. Thus, the output rate from the transport layer assembler is 170 kbps.
  • Error protection coder 800 receives the digital signal provided by transport layer assembler 700 and applies an error protection code (i.e., a forward error correcting code) to that signal, as discussed below.
  • the error protection code employed by coder 800 is a Reed-Solomon error protection code.
  • the bit rate of the output from the coder 800 is greater than that of the input digital signal from the transport layer assembler 700.
  • the bit rate of the output from the coder 800 is twice that of the input signal (340 kbps as compared to 170 kbps).
  • Interleaver 900 receives the output digital signal of the error protection coder 800 and interleaves bits of the digital signal to provide enhanced robustness against burst-like channel errors. The structure and operation of interleaver 900 are discussed below.
  • the output of interleaver 900 is a digital signal which is provided to a multiplexer 1000.
  • Multiplexer 1000 is a conventional device which combines the output signal of interleaver 900 and with signals which accomplish framing, synchronization, and equalization. By virtue of the multiplexing of such signals, the bit rate is increased (e.g., by 20 kbps raising the illustrative bit rate to 360 kbps).
  • the output of multiplexer 1000 is provided to a conventional 4 ⁇ PSK modulator 1100.
  • the output of modulator 1100 is provided to conventional band-limiting, pulse shaping circuitry 1300.
  • the signal generated by pulse shaping circuitry 1300 takes up a 200 kHz IF band.
  • Pulse shaping circuitry 1300 generates a signal suitable for transmission by conventional RF transmitter 1400 (which includes an antenna not shown). Transmitter 1400 then transmits this signal over a predetermined 200 kHz band in the 88-108 MHz FM radio spectrum.
  • receiver 20 of the illustrative digital audio broadcast system 1 comprises components which, in large part, accomplish the inverse of the functions accomplished in the transmitter 10.
  • RF receiver 1500 (which includes a receiving antenna not shown) receives a 200 kHz signal in the FM radio band (which signal was transmitted by transmitter 10) and generates a 200 kHz IF signal in conventional fashion.
  • This 200 kHz signal is applied to a conventional equalizer 1600.
  • the output of equalizer 1600 is provided to conventional 4 ⁇ PSK demodulator 1700 to produce a digital signal which comprises audio; auxiliary and ancillary data signals; and framing, synchronization, and equalization signals.
  • the digital signal from demodulator 1700 is provided to conventional demultiplexer 1800 which operates to remove from the digital signal the framing, synchronization, and equalization signals (which were added to the combined audio and data signal by multiplexer 1000 of transmitter 10).
  • demultiplexer 1800 The output of demultiplexer 1800 is therefore a digital audio and data signal. Because transmitter 10 employed interleaver 900 in generating a digital signal for transmission, receiver 20 employs a conventional complementary deinterleaver 1900 to provide the inverse operation to interleaver 900. The output of deinterleaver 1900 is thus a deinterleaved digital audio and data signal.
  • the output of the deinterleaver 1900 is provided to an error protection decoder 2000.
  • Decoder 2000 performs the inverse operation of the Reed-Solomon error protection coder 800. This decoding reduces the bit rate of the digital audio and data signal. Illustratively, the bit rate is reduced from 340 kbps to 170 kbps.
  • the error protection decoder 2000 generates a block error flag in response to errors detected by the decoder 2000 itself and any other devices of the DAB system.
  • Transport layer disassembler 2200 performs the function of separating ancillary data signals and the block error flag from the balance of the output of the error protection decoder 2000 -- that is, the audio signals and the auxiliary data signals.
  • the balance of decoder 2000 output is provided at a bit rate of 160 kbps.
  • the block error flag, the audio signals, and the auxiliary asynchronous data signals are provided to audio decoding system 2400. Assuming that no error flag is present, audio decoding system 2400 separates the auxiliary asynchronous data signals from audio signals. Thereafter, the decoder system 2400 applies an audio decoding technique to produce uncompressed digital audio output signals. The uncompressed digital audio output signals are then made available to an audio interface 2900. Assuming the presence of a block error flag, an error concealment procedure is implemented by the PAC decoder 2400 to mitigate against the effects of the block error.
  • Audio interface 2900 converts the digital audio output signals from audio decoding system 2400 into analog stereo signals suitable for use by conventional analog audio electronic equipment.
  • the transport layer assembler 700 receives a first signal 701.
  • the transport layer assembler 700 also receives an second signal 704.
  • the first signal 702 and the second signal 704 may be a perceptually encoded signal 702 and an asynchronous signal 704, respectively.
  • the perceptually encoded signal 704 may be encoded according to any one of a number of perceptual techniques in a perceptual encoder.
  • the perceptually encoded signal 701 is represented by a plurality of perceptually encoded blocks, 706, 708, 710, and 712. There are a number of bits, e.g., 714, 716, and 718, in each perceptually encoded block.
  • perceptually encoded blocks 706 - 712 represent equal-duration portions of an analog signal, the number of bits in any two blocks is not necessarily the same. For example, the number of bits in block 712 is different than the number of bits the other blocks shown (706 - 710). This is because the time portions of the analog signal represented by blocks 706 - 712 differ in perceivable information content.
  • a block with less perceivable information content, e.g., 712 may be encoded using fewer bits than a block with more perceivable information content, e.g., 706.
  • the asynchronous signal 704 is also represented digitally.
  • the digital output signal 720 is comprised of blocks 722, 724, 726, and 728 which correspond to the combination of blocks 706, 708, 710, and 712 with the asynchronous data signal 704.
  • the blocks (722 - 728) comprising the digital output signal 720 were produced in a selective combiner 730 (see Figure 2) and may be referred to "superblocks" wherein each superblock is an N i -bit output block.
  • a plurality of superblocks 722 - 728 is shown in Figure 4.
  • the order of superblocks 722 - 728 is determined according to the time sequence in which the decoded blocks must be, e.g., "played” if the superblocks 722 - 728 represent, e.g., music or voice. This ensures that a listener at the receiver will be able to understand the decoded signal.
  • the selective combiner 730 is used to generate a sequence of N i -bit output blocks 722 - 728 each of which contain a respective one of the perceptually encoded blocks 706 - 712. Further, the selective combiner 730 operates such that at least one of the N i -bit output blocks 722 - 728 comprises a portion of each of the plurality of superblocks 722 - 728.
  • the transport layer disassembler 2200 that is part of the receiver 20 performs the mirror image of the process that has been described above with reference to Figure 2. More specifically, the transport layer disassembler 2200 functions to parse a received form of the digital output signal 720 into a received asynchronous signal and a received perceptually encoded blocks.
  • the received perceptually encoded blocks represent an audio signal (e.g., music, voice, etc).
  • the received asynchronous signal represents any type of information that is representable asynchronously, e.g., stock quotes, sports scores, the name/artist of a particular song, etc.
  • the digital output signal 720 is comprised of the plurality of superblocks or N i -bit output blocks 722 - 728.
  • Superblock 726 is comprised of only perceptually encoded block 710.
  • NU i equals N i . Therefore, NA i corresponding to perceptually encoded block 708 is zero for superblock 726.
  • most superblocks, e.g., 722 comprise a perceptually encoded block 706 and NA i bits representing information, such as the second signal, "junk" data, or a combination of the two.
  • NA i bits are shown as contiguous, it is apparent that they do not have to appear in that fashion in a given superblock.
  • the transport layer is the transport layer
  • the transport layer assembler 700 adds a transport layer, e.g., 702, onto each superblock, e.g., 724.
  • a transport layer, e.g., 702 may be added to a digital representation of a signal.
  • a digital representation of an analog signal may operated upon by receiving the digital representation comprising a set of digital blocks.
  • Each digital block in the set of digital blocks has a structure.
  • the transport header comprises information on the structure of the block.
  • transport layers e.g, 702 and 703
  • transport layers e.g, 702 and 703
  • transmission of digital data results in the corruption of the digital data that is received by the receiver 20 at the far end of a transmission channel.
  • Data corruption can be accounted for by at least two different approaches. Some of the known approaches encode in such a way as to minimize the effects of the expected corruption. Others embed information which is not a part of the digital representation of the program material per se.
  • the recovery of desirable data/material e.g., a set of superblocks
  • the invocation of the error recovery mechanism(s) are interdependent. Sometimes, the process of recovering the desirable data/material and the process of invoking the error recovery mechanism(s) are one in the same.
  • the invocation of the error recovery mechanism(s) must precede the start of the recovery of the desirable data/material.
  • the start of the recovery of the desirable data/material must precede the invocation of the error recovery mechanism(s).
  • the system of Figure 1 utilizes an independent transport layer of a type which, although generally known in the computer data communication art, has not been heretofore recognized as being able to be used advantageously in the program-material-encoding context.
  • the transport layer hereof is characterized by the addition of information to each of a succession of blocks of encoded program material which is independent of the information within its respective block of encoded program material.
  • the transport layer is easily separated from the digital representation.
  • less memory is needed for storage (i.e., one stores only the digital representation instead of the digital representation with embedded information).
  • transport layer is independent of the content of digital representation, one can change the content of the digital representation without changing the transport layer.
  • the transport layer disassembler 2200 strips away the transport layer 702 from the superblock 724.
  • the effect of the transport layer assembler 700 and the transport layer disassembler 2200 will be shown for only two superblocks, e.g., 722 and 724.
  • the transport layer assembler 700 forms a plurality of transmittable blocks (see reference numerals 738 and 740 of Figure 5), for ease of understanding, the plurality of superblocks 722 - 728 was shown in Figure 4 to include the addition of NA i bits where appropriate (e.g., superblock 722 but not superblock 726) which are part of the transport layer (see Figure 5).
  • Figure 4 does not show the entire transport layer.
  • a "superblock” comprises perceptually encoded data and a portion of the transport layer
  • a "transmittable block” comprises perceptually encoded data and the entire transport layer.
  • superblocks 722 and 724 are shown as being combined with other portions of the transport layer 702.
  • the NA i bits added to the plurality of superblocks 722 - 728 are part of the transport layer.
  • the other portions of the transport layer 702 with which superblocks 722 and 724 are combined are: (1) a synchronization pattern 730; (2) a set of pointers to current important audio bits 732 for the current perceptually encoded block; (3) a set of pointers to future important audio bits 734 for the next perceptually encoded block; and (4) a set of ancillary data 736.
  • the combination of superblocks 722 and 724 with transport layers 702 and 703, respectively, is not necessarily shown to scale in Figure 5. The combinations result in transmittable blocks 738 and 740.
  • the synchronization pattern 730, the set of pointers to current important audio bits 732 for the current perceptually encoded block, the set of pointers to future important audio bits 734 for the next perceptually encoded block, and the set of ancillary data 736 typically does not change in bit length and location from transmittable block to transmittable block (e.g., from 738 to 740).
  • reference numerals 730, 732, 734, and 736 will be used to show these features for both transmittable blocks 738 and 740.
  • the only exception to the typical case occurs if the set of ancillary data 736 does not yield transmittable blocks having an integer number of bits or bytes.
  • the set of ancillary data 736 varies by a bit or a byte in order to provide an exact average rate of the ancillary data input into the transport layer assembler 700 as shown in Figure 1.
  • the synchronization pattern 730 provides a recognizable bit pattern that signifies the beginning of each transmittable block, e.g., 722.
  • the set of pointers to current important audio bits 732 points to: (1) the perceptually encoded block's 706 first bit via line 742; and (2) the perceptually encoded block's 706 first bit of a second channel (e.g., the "left" and/or “difference” channel) via line 744.
  • the set of pointers to current important audio bits 732 describes the location and amount of the auxiliary data in transmittable block 738.
  • the set of pointers to future important audio bits 734 points to: (1) the perceptually encoded block's 708 first bit via line 746; and (2) the perceptually encoded block's 708 first bit of a second channel (e.g., the "left” and/or "difference” channel) via line 748.
  • the set of pointers to future important audio bits 734 describes the location and amount of the auxiliary data in transmittable block 740.
  • the set of ancillary data 736 comprises bits that signify the amount of ancillary data followed by the ancillary data itself.
  • the synchronization pattern 730 for transmittable block 740 contains the same type of information and thus, does not require a detailed discussion. However, it should be noted that the pointers in transport layer 703 will point to places in transmittable blocks "i+1" and “i+2" as opposed to blocks "i” and "i+1.”
  • the transport layer 702 has been referred to as including the ancillary and auxiliary data. What is meant by this is that the transport layer incorporates the ancillary and auxiliary data into the transmittable block.
  • the DAB system use an error protection system comprising a number of subsystems. Some subsystems are in the transmitter 10 and some are in the receiver 20.
  • the transport layer assembler 700 relates to error protection in that it adds the synchronization pattern 730. Also, the transport layer assembler adds the set of pointers to future important audio bits 734 pointing to audio bits in the future transmittable block, e.g., the next block, via lines 746 and 748 shown in Figure 5 and also adds the set of pointers to current important audio bits 734 pointing to audio bits in the current transmittable block. More specifically, the pointers provide entry points into the PAC bit stream 701 where bit parsing may be started. This enables the transport layer disassembler 2200 to identify and typically correct errors in the pointers to the set of both current (734) and future important audio bits 736.
  • a second layer of error protection is implemented in the transmitter 10 of Figure 1 by the error protection coder 800.
  • the second layer is, illustratively, a Reed-Solomon coder.
  • a first layer of error protection is implemented by the error protection decoder 2000.
  • the first layer performs the inverse function of the second layer of error protection implemented in the transmitter 10 and is, illustratively, a Reed-Solomon decoder.
  • the Reed-Solomon decoder also generates an error flag if it is unable to successfully correct errors in a Reed-Solomon data block.
  • a second layer of error protection is implemented the transport layer disassembler 2200.
  • the second layer performs the inverse function of the first layer of error protection implemented in the transmitter 10 and, illustratively, replaces any corrupted data in the set of pointers to current important audio bits 734 by using the uncorrupted data in the set of pointers to future important audio bits 736. If both sets of pointers are corrupted, the transport layer disassembler 2200 mutes the receiver's 20 output.
  • a third layer of error protection is also implemented by the transport layer disassembler 2200.
  • the third layer of error protection may be described as functioning to conceal errors.
  • the manner in which the third layer conceals errors may be performed in a variety of manners.
  • the third layer, and how it corrects errors will be described with respect to a two-channel (e.g., a left channel and a right channel) coding system, the concepts of how to correct errors are readily extendible to multichannel systems (e.g., 5 channels) and to other two channel systems (e.g., a sum channel and a difference channel).
  • one function of the receiver' s 20 first layer is to identify the location, if any, of errors and generate an error flag where appropriate.
  • the third layer can determine, based upon the error flag, which information is intact and which must be discarded.
  • This error flag is used by the second layer to determine if alternate information from the second layer (e.g., pointers to future important audio bits) is necessary in order to perform the decoding or synchronizing functions, and what part of the perceptually encoded audio data, auxiliary data, or ancillary data is impaired.
  • the third layer is activated if the perceptually encoded audio data is in fact impaired.
  • the third level is activated, several strategies may be used, depending on the previous history of errors and the region of impaired data within the perceptually encoded audio data.
  • the decoder output is muted, and kept muted until a predetermined number of unimpaired and decoded blocks is counted, with no intervening errors.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Theoretical Computer Science (AREA)
  • Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
EP94308909A 1993-12-15 1994-12-01 Codage perceptuel de signaux audio avec allocation des bits non-utilisés à un canal de données Withdrawn EP0658984A2 (fr)

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US167711 1988-03-14
US16771193A 1993-12-15 1993-12-15

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JP (1) JPH07202825A (fr)
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CA (1) CA2135415A1 (fr)

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EP1107233A2 (fr) * 1999-12-10 2001-06-13 Sony Corporation Formatage compatible pour le codage de signaux audio
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WO1997031440A1 (fr) * 1996-02-26 1997-08-28 Nielsen Media Research, Inc. Transmission simultanee de signaux auxiliaires et audio par codage perceptif
US6035177A (en) * 1996-02-26 2000-03-07 Donald W. Moses Simultaneous transmission of ancillary and audio signals by means of perceptual coding
EP1107233A2 (fr) * 1999-12-10 2001-06-13 Sony Corporation Formatage compatible pour le codage de signaux audio
EP1107234A2 (fr) * 1999-12-10 2001-06-13 Sony Corporation Procédé de formatage d'un flux de données audio
EP1107234A3 (fr) * 1999-12-10 2001-08-29 Sony Corporation Procédé de formatage d'un flux de données audio
EP1107233A3 (fr) * 1999-12-10 2002-05-02 Sony Corporation Formatage compatible pour le codage de signaux audio
US6518891B2 (en) 1999-12-10 2003-02-11 Sony Corporation Encoding apparatus and method, recording medium, and decoding apparatus and method
CN102255680A (zh) * 2011-07-12 2011-11-23 北京海尔集成电路设计有限公司 自动切换数字音频广播信号和调频信号的方法和装置
CN102255680B (zh) * 2011-07-12 2013-01-30 北京海尔集成电路设计有限公司 自动切换数字音频广播信号和调频信号的方法和装置

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US5825976A (en) 1998-10-20
CA2135415A1 (fr) 1995-06-16
JPH07202825A (ja) 1995-08-04
KR950022169A (ko) 1995-07-28

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